Frame of reference registration system and method

ABSTRACT

A system for assisting in work carried out on a workpiece and having a frame of reference. The system includes a referencing arrangement to register the position of a first location in the frame of reference of the system; a tool holder for holding a tool to assist with the work; a data interface to receive image data relating to the workpiece; and a processing arrangement to register the image data within the frame of reference of the system. The position of the tool holder is known within the frame of reference of the system. The image data represents an image which is indexed by position relative to the first location. The processing arrangement utilizes the relative position of the image represented by the image data with respect to the first location and the position of the first location in the frame of reference of the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of registration of a workpiecewithin a frame of reference. In particular, the present inventionrelates to the registration of the location of a workpiece within theframe of reference of a robot or other device utilizing one or morepreviously acquired images of the workpiece.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 37 CFR 1.98.

When a workpiece is to be acted upon it is sometimes necessary toregister the actual location of the workpiece with images thereof toensure that any work is carried out on a correct region of theworkpiece. For example, an image of the internal structure of theworkpiece may be acquired and used as a guide when work is carried outon part of the internal structure of the workpiece which is notexternally visible.

In such instances, the frame of reference used to acquire the images ofthe workpiece must be matched with the frame of reference in whichsubsequent work is carried out such that it is possible to direct a toolon or in the workpiece to act upon an area of interest (such as part ofthe internal structure of the workpiece). The tool may be directed toutilize images of the workpiece which are acquired earlier; however,directing a tool in this manner is difficult because the actualorientation of the workpiece is usually different to the orientation ofthe workpiece when the earlier images were acquired. In addition, theformat of the images may not be conducive to such work. For example,image slices of a workpiece may depict the workpiece in its actualorientation but directing a tool based upon image slices may not be aneasy procedure.

Generally, in order to register images of a workpiece with thesubsequent location of the workpiece it is necessary to utilize featuresof the workpiece which are visible in both the image and in a view ofthe actual workpiece.

Alternatively, fiducial markers may be attached to the workpiece suchthat they are visible on the external surface thereof. The location ofthese markers within the images can be registered with the actuallocation of the markers on the workpiece and, thus, the location andorientation of the workpiece can be determined and matched with theimages.

For example, such techniques are utilized in surgical operations duringwhich images are initially acquired using an MRI or CT scanner (or otherimaging device/modality) to record the internal structure of part of apatient Fiducial markers are adhered to the patient's skin or embeddedin one of the patient's bones. These fiducial markers are visible in theMR or x-ray CT images which are obtained during the scanning process.Subsequently, a surgical operation is carried out on the patientutilizing the MRI or x-ray images.

The use of fiducial markers and similar techniques introduces a numberof problems. For example, if the fiducial markers become displaced, thenthe actual location of the workpiece (or patient in the example providedabove) cannot be accurately registered within the frame of reference ofthe robot or matched with the images of the workpiece which werecaptured earlier.

In addition, the processing techniques required to register theworkpiece within the frame of reference to the robot are complex andoften take a considerable amount of time to complete.

The present invention seeks to ameliorate the problems associated withthe prior art.

BRIEF SUMMARY OF THE INVENTION

A system for assisting in work carried out on a workpiece and having aframe of reference. The system includes a referencing arrangement toregister the position of a first location in the frame of reference ofthe system; a tool holder for holding a tool to assist with the work; adata interface to receive image data relating to the workpiece; and aprocessing arrangement to register the image data within the frame ofreference of the system. The position of the tool holder is known withinthe frame of reference of the system. The image data represents an imagewhich is indexed by position relative to the first location. Theprocessing arrangement utilizes the relative position of the imagerepresented by the image data with respect to the first location and theposition of the first location in the frame of reference of the system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In order that the present invention maybe more readily understood,embodiments thereof will be described, by way of example, with referenceto the accompanying drawings.

FIG. 1 shows a perspective view of a CT scanner.

FIG. 2 shows a perspective view of a table for use with an imageacquisition device, such as a CT or MRI scanner.

FIG. 3 shows a perspective view of a robot according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention shall now be described by way of reference to asurgical operation in which the workpiece is a patient. However, it willbe appreciated that the present invention is equally applicable to usein relation to other workpieces and other procedures. For example,embodiments of the present invention could be utilized within amanufacturing facility or as part of a automated production line.

Prior to a surgical operation, a patient may be scanned to obtaininternal images of an area of the patient's body. For example, images ofa patient's spine may be acquired prior to an operation to correct adeformity or to treat a trauma. An example of a CT scanner 1,2 is shownin FIG. 1.

It will be appreciated that the type of imaging device utilized toobtain images of the patient will be dependent upon a number of factors.These factors include the availability of the imaging devices, the typeof information required, the characteristics of the patient, and thecost associated with the use of the device.

Many imaging devices acquire images using standard file formats in whichimage slices of a patient (usually sagittal, coronal or axial) aredirectly related to the position of the bed 2 (or “table”) —on which thepatient is placed—within the device when the images are acquired (ie.the image data is indexed with respect to the relative position of thetable 2). FIG. 2 shows a typical table 2 in a second position (FIG. 1which includes a view of a CT scanner 1 shows the table 2 in a firstposition).

In some devices, each image voxel may be associated with a coordinatevalue representing its location in three dimensional space relative to alocation on the table 2. This includes examples of devices in which eachimage slice is associated with a value representing the position of thetable 2 with respect to the imaging device when the slice was acquired.In this instance, each voxel is associated with three dimensionalcoordinates by virtue of its position within the particular image slice(i. e. its two dimensional position within the image) and the valueassociated with the slice.

An example of a file format which is utilized by many imaging devices isthe Digital Imaging and Communications in Medicine (DICOM) file formatand, more specifically, version three of that file format.

This file format has been widely introduced so that images obtainedusing different imaging devices (which need not be different types ofimaging device) can be processed and manipulated by many differentdevices, including peripheral equipment.

Example imaging techniques or modalities which are supported by theDICOM file format include: computed topography (CT), magnetic resonance(MR), ultrasound and computed radiography (CR). It will be appreciatedthat there are a vast number of additional modalities which aresupported by file formats, such as the DICOM file format. The presentinvention is not limited by the specific use of the DICOM file formatwhich is merely utilized as an example of a suitable file format. Nor isthe present invention limited to the use of a particular modality orimaging device.

If a tool holder, robot, tool or other device 3 is placed in a positionrelative to the table 2 on which the patient was placed during thepreparatory image acquisition process (as discussed above and shown inFIG. 3), then the table position can be determined relative to the robot3 (or other device). This information can be utilized to register thelocation of the patient within the frame of reference of the robot bymatching the current table position with table position in at least oneof the image slices which were acquired during the image acquisitionprocess, the images being referenced with respect to a known location onthe table 2.

Using this technique, each voxel within a three-dimensional image(comprising, for example, a number of image slices) of the patient whichwas acquired during the image acquisition process may be registered to aphysical three-dimensional co-ordinate within the frame of reference ofthe robot 3. Thus, it is possible for the robot 3 to carry out delicatework on the patient with a reduced risk of error.

In order to minimize the problems associated with the patient movingrelative to the table 2, after the image acquisition process, but beforethe surgical operation (or “intervention”), it is preferable to carryout any surgical procedure within the vicinity of the imaging device,for example, within the scanner suite in which the images are acquired.

The placement of a robot 3 in a location relative to the position of thetable 2 utilized in the image acquisition process such that the positionof the table 2 may be registered within the frame of reference of therobot 3 can be achieved in a number of different manners. For example,the robot 3 can be permanently attached to the table 2 at a knownlocation. In such an instance, the robot 3 may also be subjected to theimage acquisition process. It will be appreciated that it may bedifficult to utilize such a robot 3 in conjunction with certain imagingdevices, for example, in an MRI, strong magnetic fields could make theuse of a permanently attached robot 3 difficult.

Furthermore, in a number of imaging devices, the table on which thepatient is placed must be passed through a bore in the scanning device.This places severe restrictions upon the dimensions of any robot 3 whichis permanently attached to the table. Furthermore, a robot 3 of thistype may cause an obstruction to the imaging device.

Alternatively, it is possible to attach the robot 3 temporarily to thetable after the scanning process. This can be achieved by providing anattachment arrangement (not shown) on the table 2 at a known locationand a corresponding attachment arrangement 4 on part of a robot 3.

Preferably, the robot 3 is separate from the scanner table 2 and movedinto a position generally adjacent to the table 2. The robot 3 may befreestanding and self-contained (with the possible exception of a powersupply). In this instance, the robot 3 includes a referencingarrangement 4 such that it is possible to register the position of thetable 2 within the frame of reference of the robot 3 by utilizing thereferencing arrangement 4.

The referencing arrangement 4 could take a number of forms. For example,the arrangement 4 may include one or more location registering elementswhich can be abutted against one or more corresponding locating elementson the table. The one or more location registering elements of the robot3 may have a fixed location with respect to the location of the robot 3or may moveable with respect to the location of the robot (or acombination of both).

In the latter case, the position of the location registering elements ofthe robot 3 can, according to one aspect of the invention, be determinedusing magnetically encoded tape along a surface which is fixed withrespect to the location of the robot 3. Movement of a locationregistering element, in such an arrangement, would cause a correspondingmovement in a magnetic information reading device (or decoder) suitableto read the encoded tape such that the location of the element can bedetermined with respect to the location of the robot. It will beappreciated that additional referencing arrangements 4 may be needed ifthe location registering elements can move in more than one axis.

Other referencing arrangements 4 include the use of laserinterferometry, triangulation techniques, stereo images (captured by,for example, one camera moved to multiple locations or by two or morecameras), and contact or non-contact trigger probes (or other metrologytechniques). In some instances, a tool 5 attached to an arm 6 of therobot 3 is maneuvered into a position such that the tool 5 is in contactwith a known location on the table 2. Alternatively, at least part ofthe robot 3 may be inserted into the imaging device and the resultantimage of the part of the robot 3 can be used for referencing, combinedwith knowledge of its own position from its joint encoders.

In other embodiments of the present invention, the robot 3 has areferencing arrangement 4 comprising one or more fixed receptacles orsurfaces into which or against which at least part of the table 2 can beplaced. It will be appreciated that such surfaces or receptacles couldbe used to register the location of the table 2 within the frame ofreference of the robot 3.

It will be understood that the method used to register the position ofthe table 2 in the frame of reference of the robot 3 can take a numberof forms. The arrangements provided above are merely examples of suchmethods.

The referencing can occur while the patient and table 2 are still withinor close to the imaging device. The table 2 can then be moved out of theimaging device to allow more access to the patient. The movement of thetable 2 can be recorded, for example, by the imaging device and thisinformation passed to the robot 3. Therefore, a table 2 which has beenregistered within the frame of reference of the robot 3 in a firstposition may be subsequently moved to a second position and the movementrecorded. The robot 3 will be able to adjust the position of the table 2within its frame of reference without the need to re-register thelocation of the table 2 by using the recorded movement information.

Once the location of the table 2 has been registered within the frame ofreference of the robot 3, then previously acquired image information canbe matched with the known location of the table 2 to register thelocation of the patient (i.e. the workpiece) within the frame ofreference of the robot 3. This information is acquired though a datainterface 7.

The data interface 7 may be directly linked to an imaging device or maycomprise a connection to a network (such as an Ethernet connection). Theinterface may be wired or wireless.

The robot 3 uses the coordinate information associated with the voxelsin the image information to register the location of the patient withinits frame of reference. In other words, the robot 3 uses the knownlocation of the table 2 with information which relates to the positionof the patient on the table 2, in order to determine the actual locationof the patient.

A robot 3 according to an embodiment of the present invention may,therefore, comprise one or more referencing arrangements 4 (to determinethe location of the table with its frame of reference), a data interface7 (to receive information concerning the images acquired during theimage acquisition process and information concerning any movements ofthe table), and a processing arrangement (not shown) suitable toregister the location of the table 2 within the frame of reference ofthe robot 3 and match the image information with the frame of reference.Preferably, the processing arrangement allocates one or morethree-dimensional coordinate values within the frame of reference of therobot 3 (i.e. potentially different coordinate values to thoseassociated with the voxel and stored in the image information) to one ormore respective voxels of the images.

The robot 3 advantageously includes one or more tools 5, or toolattachment arrangements (not shown) to accept tools 5. The tools 5 aresuitable to act on the patient. After the patient has been registeredwithin the frame of reference of the robot 3, the robot 3 can operate toperform a task in relation to the patient.

The term “robot” has been used above; however; this term is intended toinclude fully and semi-automated devices capable of controlling,assisting or actually working on a workpiece (e.g. a patient). Thesystem need not, however, include a robot, and may, for example,alternatively include a passive tool holder. A tool held by the toolholder may itself comprise a surgical robot.

In some embodiments of the present invention, the robot 3 is alsooperable to locate one or more features of the workpiece or one or morefiducial markers (not shown) attached to or placed on the workpiece toaid in the registration process.

It will be appreciated that the table 2 is only an example of a firsttype of object relative to which a workpiece (or second type of object)may be located. A workpiece can be placed relative to any known location(to form the basis of the coordinate values of the image information) solong as the robot 3 can determine the location of a point which has aknown position (by virtue of, for example, a coordinate value) withrespect to the known location. In other words the robot 3 must be ableto determine the basis on which the coordinates associated with theimage voxels has been made (this usually requires information about thelocation of the origin of the coordinate system and the spacing ofcoordinate values).

When used in this Specification and Claims, the terms “comprises” and“comprising” and variations thereof mean that the specified features,steps or integers are included. The terms are not to be interpreted toexclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the followingClaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilized forrealizing the invention in diverse forms thereof.

1. A system for assisting in work carried out on a workpiece and havinga frame of reference, the system comprising: a referencing arrangementmeans to register a position of a first location in said frame ofreference; a tool holder means for holding a tool to assist with work,said tool holder means having a position known within said frame ofreference; a data interface means to receive image data relating to saidworkpiece, said image data representing an image indexed by positionrelative to said first location and being comprised of a plurality ofvoxels; and a processing arrangement means to register said image datawithin said frame of reference by utilizing a relative position of saidimage represented by said image data with respect to said first locationand a position of said first location in said frame of reference.
 2. Thesystem according to claim 1, wherein said tool holder means comprises arobot.
 3. The system according to claim 2, wherein said robot is amedical robot.
 4. The system according to claim 1, wherein saidreferencing arrangement means comprises a laser interferometer.
 5. Thesystem according to claim 1, wherein said referencing arrangement meanscomprises a triangulation device.
 6. The system according to claim 1,wherein said referencing arrangement means comprises one or moresurfaces for abutment against part of an object associated with saidfirst location.
 7. The system according to claim 1, wherein said datainterface means is compatible with said image data in DICOM 3 fileformat.
 8. The system according to claim 1, wherein said data interfacemeans is operable to receive image data in the form of image slices,each image slice being indexed by position with respect to said firstlocation.
 9. The system according to claim 1, further comprising: areferencing adjustment arrangement means to adjust a position of saidfirst location within said frame of reference as a result of informationconcerning a movement of said first location.
 10. A method ofregistering image data within a frame of reference of a system, saidsystem being comprised of a tool for assisting in work carried out on aworkpiece, and a tool holder, said tool being held by said tool holder,said tool holder having a position known within said frame of reference,the method comprising: registering a position of a first location insaid frame of reference; receiving image data relating to saidworkpiece, said image data representing an image indexed by positionrelative to said first location and being comprised of a plurality ofvoxels; and registering said image data within said frame of referenceby utilizing a relative position of said image represented by said imagedata with respect to said first location and a position of said firstlocation in said frame of reference.
 11. The method according to claim10, wherein said tool holder is comprised of a robot.
 12. The methodaccording to claim 11, wherein said robot is a medical robot.
 13. Themethod according to claim 10, further comprising: registering a positionof said first location by a laser interferometer.
 14. The methodaccording to claim 10, further comprising: registering said position ofsaid first location by a triangulation device.
 15. The method accordingto claim 10, further comprising: registering said position of said firstlocation by providing one or more surfaces for abutment against part ofan object associated with said first location.
 16. The method accordingto claim 10, wherein said image data is in Dicom 3 file format.
 17. Themethod according to claim 10, wherein the step of receiving image datacomprises receiving image data formed into image slices, each imageslice being indexed by position with respect to said first location. 18.The method according to claim 10, further comprising: acquiring imagedata using an image acquisition device.
 19. The method according toclaim 18, wherein the step of acquiring image data comprises the step ofacquiring image data and acquiring image data of said tool holder means.20. The method according to claim 10, further comprising: adjusting aposition of said first location within said frame of reference of systemas a result of information received by a system concerning a movement ofsaid first location. 21-22. (canceled)